The present disclosure relates, in various exemplary embodiments, generally to photoreceptors or imaging members for electrophotographic or xerographic processes. More particularly, the present disclosure relates to a multi-layered photoreceptor or imaging member that includes an undercoat layer adjacent to a substrate, where the undercoat layer includes at least a non-porous anodized aluminum barrier overlay coating.
In an electrophotographic application such as xerography, a charge retentive surface (i.e., photoconductor, photoreceptor, or imaging surface) is electrostatically charged and exposed to a light pattern of an original image to be reproduced to selectively discharge the surface in accordance therewith. The resulting pattern of charged and discharged areas on that surface form an electrostatic charge pattern (an electrostatic latent image) conforming to the original image. The latent image is developed by contacting it with a finely divided electrostatically attractable powder referred to as “toner.” Toner is held on the image areas by the electrostatic charge on the surface. Thus, a toner image is produced in conformity with a light image of the original being reproduced. The toner image may then be transferred to a substrate (e.g., paper), and the image affixed thereto to form a permanent record of the image to be reproduced. Subsequent to development, excess toner left on the charge retentive surface is cleaned from the surface.
The aforementioned process is known, and useful for light lens copying from an original, and printing applications from electronically generated or stored originals, where a charged surface may be image-wise discharged in a variety of ways. Ion projection devices where a charge is image-wise deposited on a charge retentive substrate operate similarly.
Electrophotographic imaging members are commonly multilayered photoreceptors that include a substrate support, an optional electrically conductive layer, an optional charge blocking layer, an optional adhesive layer, a charge generating layer, a charge transport layer, and an optional protective or overcoating layer(s). The photoreceptor or imaging members can take several forms, including flexible belts, rigid drums, and the like.
In multi-layered photoreceptors or imaging members, an undercoat layer is often deposited between the substrate and a photosensitive or imaging layer(s) to enhance the physical and/or electrical properties of the photoreceptor. For example, an undercoat layer may be used to provide dielectric strength or conductivity to the photoreceptor, provide mechanical adhesion strength between the substrate and the photosensitive layer(s), and to improve cyclic stability of the photoreceptor. An undercoat layer may also be utilized to provide charge blocking capabilities and, for example, prevent holes from being injected from the conductive layer to the opposite photoconductive layer(s).
Additionally, an undercoat layer may also be utilized to prevent light-scattering, plywood defects. The use of coherent illumination sources in conjunction with multilayered photoreceptors results in a print quality defect known as the “plywood effect” or the “interference fringe effect.” This print defect consists of a series of dark and light interference patterns that occur when the coherent light is reflected from the interfaces that pervade multilayered photoreceptors. The plywood effect in organic photoreceptors generally results from the reflection from the air/charge transport layer interface, i.e., the top surface, and the reflection from the undercoat layer or charge blocking layer/substrate interface, i.e., the substrate surface. The effect can be eliminated if the strong charge transport layer surface reflection, or the strong substrate surface reflection, is reduced or suppressed.
Typically, the undercoat layer in many multilayered photoreceptors is a resin layer. The resin layer is generally formed of, for example, a mixture of acetyl acetone zirconium tributoxides, and gamma amino propyltriethoxysilane, casein, polyvinyl alcohol, nitro cellulose, ethylene acrylic acid copolymer, polyamide (nylon 6, nylon 615, nylon 610, copolymerized nylon, alcoxy mentholated nylon, and the like), polyurethane, gelatin, and like materials.
The undercoat resin layers, however, often exhibit poor environmental cyclic stability due to the fact that the volume resistivity of a resin greatly depends on the ionic conductivity and is strongly affected by temperature and humidity conditions. Additionally, conventional undercoat layers that employ light-scattering particles have a limited range of suitable materials that may be used as the light-scattering particles. Many polymeric materials have the particle size, density and dispersion stability in the proper range, but have refractive index values that are too close to the binder resin used in the undercoat layer. Light-scattering particles having a refractive index similar to a binder refractive index may produce light scattering insufficient to eliminate the plywood effect in the resulting prints.
It is thus desirable to provide material, suitable for use as an undercoat layer in a photoreceptor in an imaging device, which exhibits beneficial properties and contributes to the performance of the imaging member. It is further desirable to provide an undercoat layer for a photoreceptor with properties that will contribute to extending the life of the photoreceptor. Among other things, it is desirable to provide an undercoat layer with improved corrosion resistance, enhanced hardness, and more uniform dielectric characteristics to increase the life of the photoreceptor.